Electrically chargeable particle



July 7, 1970 JETS. 4.

H. WEINSTEIN ELECTRICALLY CHARGEABLE PARTICLE Filed Dec. 29. 1967 United States Patent "ice 3,519,500 ELECTRICALLY CHARGEABLE PARTICLE Harold Weinstein, Van Nuys, Caliii, assignor to International Rectifier Corporation, El Segundo, Calif., a corporation of California Filed Dec. 29, 1967, Ser. No. 694,652 Int. Cl. H01l /00 U.S. Cl. 148-33 5 Claims ABSTRACT OF THE DISCLOSURE An electrically chargeable particle formed of monocrystalline silicon having a spherical junction therein. Incident light on the junction creates a potential difference between the concentric shells of opposite conductivity types to form a charge on the exterior of the particle.

This invention relates to electrically chargeable particles for use in xerography, or the like, and more particularly relates to a semiconductor particle having a central region of one of the conductivity types and a concentric shell of the other of the conductivity types whereby incident radiation reaching the junction creates a charge on the exterior of the particle.

A primary object of this invention is to provide a novel particle which can be charged by the application of incident radiation.

Another object of this invention is to provide a novel particle for use in xerography.

A further object of this invention is to provide a novel particle which can be moved by an electric field responsive to the application of radiation to the particle.

These and other objects of this invention will become apparent from the following description when taken in connection with the drawings in which:

FIG. 1 shows a plan view of a spherical silicon particle which has been formed to a desired diameter.

FIG. 2 is a cross-section view of FIG. 1 taken across section line 2-2 in FIG. 1.

FIG. 3 shows the particle of FIGS. 1 and 2 after the formation of a spherical P-N junction therein.

FIG. 4 schematically illustrates the development of an electric charge on the particle responsive to incident radiation thereon.

Referring first to FIGS. 1 and 2, there is shown a particle 10, generally spherical in shape of N-type monocrystalline silicon, having a resistivity of from to 10.0 ohm centimeters and a diameter of from 0.1 to 1 micron.

Specifically, a diameter of 1 micron and 2 ohm centimeters may be used. The particle is formed with a large number of similar particles by placing a monocrystalline silicon ingot of N-type material, with the desired resistivity in a suitable ball mill until particles are formed with average diameters of 1 micron. Obviously, any desired grinding or crushing operation, or the like, could be used to form the particles.

The particles are then placed on a quartz sheet which is connected to means for agitating the sheet to cause the particles to move slightly, and the particles, sheet and agitation means are placed in a gaseous diffusion furnace for the formation of spherical P-N junctions in the various particles.

A standard diffusion furnace may be used, using solid gallium in an open tube furnace with a flow of argon carrying vaporized gallium over the particles. The argon gas may flow at a rate of from 200 to 1000 liters per hour, with the furnace held to about 1200 C. for about 3,519,500 Patented July 7, 1970 1-5 minutes, depending on the particular particle size used and the depth of penetration of the junction. Preferably, the junction should have a radial depth of from 0.1 to 0.5 micron.

FIG. 3 shows the particle 3, after diffusion, having a junction 11 formed between the central N-type core and the outer P layer formed by the diffusion. In FIG. 3, particle 10 has a diameter of 1 micron and a junction depth of 0.2 micron.

Obviously, other diffusion materials and diffusion or epitaxial processes could be used, starting with N- or P-type materials.

FIG. 4 shows the manner in which the particle reacts to incident radiation 13 which could be the light of a tungsten filament. In the manner of any of the wellknown solar cells, photons of incident radiation 13 will create electron-hole pairs within the particle, for example, Within the P-type outer layer. Some electrons of the hole pairs, within a diffusion length from junction 11, will reach junction lland a corresponding number of holes will remain in the outer P-type layer to charge the outer layer positive while the interior layer is charged negatively. If the particles are placed in an electric field, the field will see a positively charged particle and the particle will be moved in the direction of the field.

This effect can then be used to cause the particles to deposit on selectively charged regions of a surface area; and have general application to any arrangement calling for being able selectively to cause particles to move responsive to application of an external control, such as the application of radiation to particles in an electric field. Note that when the radiation is not applied to the particles, they will be unaffected by the field.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. An electrically chargeable particle comprising a generally spherical particle of semiconductor material having a spherical P-N junction therein between a central core portion of one of the conductivity types and an outer shell portion of the other of the conductivity types.

2. The particle of claim 1 wherein said particle is formed of monocrystalline silicon.

3. The particle of claim 1 wherein said particle has a diameter of from 0.1 micron to 10 microns.

4. The particle of claim 1 wherein said junction has a depth of from 0.1 to 0.5 micron.

5. The particle of claim 2 wherein said junction has a depth of from 0.1 to 0.5 micron.

References Cited UNITED STATES PATENTS 5/1955 White 148-15 2/1965 Denkewalter et al. 148-33 US. Cl. X.R 

